Osteosarcoma is a malignant bone tumour. This means it originates from cells of the bone (osteocytes) mutating. It is malignant, which means it is prone to spread and will cause harm to your pet, and the prognosis is, sadly, poor.

Where do osteosarcomas occur?

The common adage for remembering osteosarcoma sites is “away from the elbow, towards the knee”. The knee joint is composed of the femur and tibia; as osteosarcomas commonly occur “towards the knee”, this means they usually affect the bottom of the femur and top of the tibia, as these bits of the bones make up the knee joint. With the elbow, it typically affects the top of the humerus, and the bottom of the radius, as it is the top of the radius and the bottom of the humerus which make up the elbow joint. Other sites include the pelvis, bottom of the tibia and top of the femur, just to confuse matters.

To summarise, common sites for an osteosarcoma include:

The humerus (forelimb)

The radius (forelimb)

The femur (hindlimb)

The tibia (hindlimb)

The pelvis (hip bones)

How would I know if my pet had an osteosarcoma?

Osteosarcomas destroy the normal bone; this can cause severe lameness, where your pet doesn’t want to use the affected leg. Osteosarcomas cause destruction, which means that the bones are not as healthy and strong as they were; for this reason, you may also see fractures which occur with very little trauma. That is to say, bones may break because they are being damaged on the inside, not because they have been forcibly broken. Sadly, these tumours are highly malignant, which means that they can spread through the body (metastasise). Approximately 90% of osteosarcomas have already spread to the lungs by the time they are detected in the bones.

To summarise, signs of an osteosarcoma include:

Generally being unwell, such as being lethargic or depressed

Lameness and pain in the affected limb

Fractures without an obvious cause (“pathological fractures”)

Lung signs; coughing, not being able to exercise as much as they were

What treatment options are there for osteosarcomas?

Osteosarcomas can be identified on X-rays, and there are a number of treatment options. However, tragically, the prognosis and outcome for each option is very poor.

Palliative care; using non-steroidal anti-inflammatory painkillers can provide a good quality of life for some osteosarcoma cases. Alternatively, steroids such as prednisolone can be used; it is anti-inflammatory and can slow the rapid progression of some types of cancers. Sadly, this will only give your pet a more comfortable time, rather than giving him more time, as it will not cure the cancer.

Amputation; removing the affected limb has around a 4 – 5 month survival time as, although you can remove the cancerous bone, spread to the lungs is very common.

Amputation and chemotherapy; this means that we remove the source of the cancer, as well as using chemotherapeutic drugs to control the spread of the cancer. This option has the best survival time at around 8 months, but occasionally chemotherapy can have unpleasant side effects, such as vomiting and diarrhoea, which can be stressful for owners and pets. Fortunately, this is much rarer in animals than side effects in humans on chemo, because we use different protocols.

Euthanasia; if an animal is in severe pain which cannot be controlled by medication, sadly, it may be time to say goodbye. Euthanasia is a relief for many animals who are in intractable pain, and although it is a sad and difficult decision, often it is the right decision for the welfare of a beloved pet.

Our vets and vet nurses will be happy to discuss palliative and end of life care, and appreciate how difficult a decision it is, and how deeply we can be affected by news of our pets having a malignant cancer.